You can make anything street legal if you try hard enough. In the case of a dirt bike you need a headlight with a battery that can operate the head-light for 20 or 30min without the bike running, taillight that is brake activated and DOT approved street tires. I am actually in the process of doing it to my RM250 but I'm going the extra mile and running blinkers, and a license plate light as well. The stator rewind he is looking for will boost the power output to allow for the added draw of the lights.

Most states require you to have flashers. If your state doesn't require signals it still may require you to have the tail-light as your flasher. Just something to look into before you take it in for inspection.